Methods of non-specific, label-free single virus detection may provide limited information about individual virions. For instance, mechanical resonance methods primarily operate on the principle of mass-loading of a resonator and the associated frequency shift and have obtained yoctogram resolution. In this manner, the mass of a particle can be estimated with high resolution, but size and density are not obtainable without additional assumptions. Photonic methods, in contrast, rely on the shift of optical resonance frequency or optical mode splitting. This provides information on the polarizability, approximate size of a nanoparticle, but does not permit further identification.